1. Combined Spectroscopy…
When identifying a compound we may not get all necessary information from a single type of spectroscopy.
Most often we combine techniques e.g. Empirical formula, mass spec and IR spec to allow us to obtain all necessary information

2. Combined Spectroscopy…
You have an unlabelled sample that is either:
Butanal
Butan-2-one
Plan how you would identify which it is:
Using spectroscopy
Using chemical tests

3. Combined Spectroscopy…
Using spectroscopy:
Identify the functional groups present using IR spectra
Predict the possible fragments for each isomer
Assign the peaks of the mass spec
Determine the nature of the compound

4. Combined Spectroscopy…

5. Combined Spectroscopy…
The two C=O peaks cannot be distinguished by their wavenumber

6. Combined Spectroscopy…
Butanal and butan-2-on have very similar fragments
e.g.
Butanal CH2CHO m/z = 43
Butan-2-one C3H7 m/z = 43
However there is (at least) one peak that tells them apart…

7. Combined Spectroscopy…
m/z = 42
-CH2CO-

8. Therefore we have Butan-2-one
Combined Spectroscopy…
Therefore we have Butan-2-one

9. Combined Spectroscopy…
Chemical test:
Reflux both samples with acidified Potassium Dichromate
Butanal shows orange to green
Butan-2-one shows no change

10. Combined Spectroscopy…
A chemist has 2 unlabelled isomer samples: propanoic acid and 1-hydroxypropan-2-one.
What information would we ideally want to be able to tell which is which?

11. Combined Spectroscopy…

12. Combined Spectroscopy…
Mass spec can be used to confirm the identity of Y as 1-hydroxypropan-2-one
m/z = 31
-CH2OH